Method of cold-forging a tubular body

ABSTRACT

A BILLET OF AT LEAST TWICE AS GREAT A DIAMETER AS ITS THICKNESS IS INSERTED INTO A MOLD HAVING A BOTTOM OF CONICAL OR SPHERICAL SHAPE AND IS PRESSED DOWNWARD BY A PUNCH HAVING A BODY END SUBSTANTIALLY CORRESPONDING IN SHAPE TO THE BOTTOM OF THE MOLD AND HAVING A SMALLER DIAMETER THAN THE DIAMETER OF THE SURROUNDING MOLD. THE TOP OF THE BILLET IS PROVIDED WITH A LUBRICANT. ON PUSHING DOWN THE PUNCH THE CENTER PART OF THE BILLET IS FIRST BENT DOWNWARDLY AFTER WHICH THE MATERIAL IS EXTRUDED UPWARDLY INTO THE SPACE BETWEEN THE PUNCH AND THE MOLD.

METHQD or coLn-FoRGING A TUBULAR BODY Filed aprill 1.7,'1968 2 Smets-sheet 1 INVENTOR. ESKH. MoN ES TAM I I Jan.l y1 2, 1,1971 r MNESTAM 3,553,994

mamon' 0F' cow-FORGI'NG A TUBULAR BODY Filed pm 17,1968]y y aaneen-sheen NVEN ESKIL MONE M United States Patent O Int. Cl. B21c 23/00 U.S. Cl. 72-43 1 Claim ABSTRACT F THE DISCLOSURE A billet of at least twice as great a diameter as its thickness is inserted into a mold having a bottom of Aconical or spherical shape and is pressed downward by a punch having -a body end substantially corresponding in shape to the bottom of the mold and having a smaller diameter than the diameter of the surrounding mold. The top of the billet is provided with a lubricant. On pushing down the punch Ithe center part of the billet is rst bent downwardly after which the material is extruded upwardly into the space between the punch and the mold.

BACKGROUND OF THE INVENTION (l) vField of the invention The present invention relates to a method of coldforging a tubular body with the help of a punch which is inserted into a mould surrounded by a pressure cylinder With a radial gap corresponding to the desired wall-thickness of the body, wherein the bottom of the mould consists of a die having a central conical and/or spherical depression, and the active end of the punch is insertable into said depression and susstantially shaped with corresponding conical and/or spherical surfaces.

A(.2) The prior Ian When cold-forging tubular bodies according to the `cup-extrusion method, the lubricant which is initially present on the billet within an area congruent with the projection of the punch on the billet constitutes the quantity of lubricant available for lubrication of the internal surface of the body during forging. When forging with a punch having a substantially plane end surface, satisfactory lubrication can be obtained even with relatively deep holes, bu-t if the forging punch is too conical or rounded at fthe end, the movement of the billet material is such that said quantity of lubricant at an early stage of extrusion is removed from the zone where lubrication 'is a necessity. It is thus not possible to forge sleeves with a bottom which is too conical or rounded in one step to any great depth.

SUMMARY OF THE INVENTION With a method according 4to the invention the depth which can be achieved is considerably increased if the billet is iirst drawn :to a bowl shape, after which the preshaped billet is extruded to the desired nal shape, which can with advantage be carried out in one and the same operation. No great increase or dissipation of the layer of lubricant occurs during drawing so that this is intact ice to be the case when manufacturing certain grenade shells.

A method according to the invention is characterised in that a disc-Shaped billet, the thickness of which is greater than said gap and at the most half the diameter of the billet, is provided with a lubricating layer intended for cold-forging and arranged to rest against the upper part of the die along a a narrow, annular supporting surface, after which the punch is pressed against the upper surface of the billet to initiate a drawing process to shape the billet in conformity with the end of the punch, during which drawing process the contact surface of the punch on the billet has at all times a diameter which is less than half the inner diameter of said supporting surface, the lower side of the billet being formed with convexity and the upper side wit-h substantially corresponding concavity, said supporting surface remaining substantially unaltered, after which the punch continues its downwards movement so that the billet material is extruded in a manner known per se into the space between the mould and the punch.

BRIEF lDESCRIPTION OF THE DRAWINGS The invention will be described in the following with reference to the accompanying drawings where FIGS. 1, 2, 3 and 4 show different stages in a manufacturing process according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawings 1 designates a punch which is mechanically connected to the pressure piston 2 of a press stand and coaxially arranged in relation to a mould 3 which is surrounded by a pressure cylinder 4 which has been put together from several parts. The bottom of the mould consists of a die 5 which has a bowl-shaped depression 6 limited by a conical surface 7 and a spherical surface 8. The active end of the punch 1 is intended to be inserted into the depression 6 and is shaped with a conical surface substantially corresponding to that of the surface 7, and a spherical surface the radius of curvature of which has approximately the same value as that of the surface 8. The die 5 is attached to an expelling punch 9 by means of the screw 10. The lpressure surface is designated 11 and a pressure-distributing plate arranged on this is designated 12.

In order for the hollow 5 to be sufficiently strong for forging it is made externally conical. During forging it is pressed down under the influence of the forging pressure into the surrounding part so that the required tension is obtained.

The forging billet 13 comprises a circular disc the diameter of which corresponds to the inner diameter in the upper part of the mould. The thickness is several times greater than the intended wall-thickness of the iinished tubular body but sufficiently small to allow tensile forces to cause a predominant part of the plas-tic deformation taking place when the punch 1 is pressed downwards as shown in FIGS. 1 and 2. This is obtained with certainty when 4the thickness of the billet is at the most equal to half its diameter and, at the same time, the internal diameter of its supporting surface is at least twice as great as the cross-measurement of the contact surface between the billet and the punch. The lubricating layer applied on the upper side of the billet is still intact at the corresponding stages. In FIG. 3 the drawing is almost completed and extrusion has commenced.

In FIG. 4, .14 designates the linished tubular body.

I claim:

1. Method of cold-forging a cup-like tubular body by backward extrusion comprising the s-teps of inserting a punch into a mold surrounded by a pressure cylinder with a radial gap between the cylindrical outside of the punch and the interior of the mold corresponding to the desired wall-thickness of the body, wherein the lowest part of the mold is closed by a `tight bottom which comprises a die having a central depression the surface of which is a surface of revolution, and the active end of the punch is insertable into said depression and is substantially shaped with a corresponding surface, providing a disc-shaped billet, the thickness of which is substantially greater than the thickness of the bottom of said cuplike body, greater than said gap and at the most half the diameter of the billet, providing a lubricating layer intended for cold-forging and arranging the billet to rest against the upper part of the die along a narrow, annular supporting surface, pressing the punch against the upper surface of the billet to -initiate a drawing process to shape the billet in conformity with the end of the punch, during which drawing process the contact surface of the punch on the billet at all times has a diameter which is less than half the inner diameter of said supporting surface, the lower side of the billet being formed with convexity and the upper side with substantially corresponding con- UNITED STATES PATENTS 1,900,665 3/1933 Prussing 72-267 429,098 5/1890 Robertson '72-267 841,954 1/1909 Frank 72-267 2,104,222 l/l938 Decker 72-260 1,413,284 4/1922 Maloney 72-256X FOREIGN PATENTS 621,535 4/l949 Great Britian.

RICHARD I. HERBST, Primary Examiner A. L. HAVIS, Assistant Examiner U.S. C1. X.R. 72-256, 267, 356 

